Newsgroups: rec.audio.tech
Subject: Re: Computer Mic to XLR
References: <[email protected]> <[email protected]> <[email protected]> <[email protected]>
[email protected] (Roger Elmore) writes:
> >Gulf Joe wrote:
> > You can totally ignore the +5v ring.  
> I don't see how I can ignore the +5V, when I need that to power the
> mic's condenser element.  

For soundcsrd microphones built using electret capsules there is
need to supply that around +5V through few kilo-ohms resistor
to the microphone in order to get any sound from them.

> The headset/mic I'm working with is a Jensen
> (MCM #83-7928).  As far as I know (could be wrong here, but why would
> SoundBlaster put +5 on the ring of their jacks since the later SB16s),
> most current PC mics are condenser and need the voltage. 

That�s true. SB16 supplies +5V to the ring though 2.2 kohm resistor.

> Creative/SB specs it's sound card's mic input at 500-600 ohms (low
> impedance) with 10-200mVpp sensitivity. I'm assuming the PC mic I'm
> using to be the same configuration, since it plugs in to the card
> directly without problems.

It is true that you can plug 600 ohms micophone to a SB16 input
and get it working somehow, but it is hard to get any usable
sound volumes in recording, because quite few dynamic microphones
with 600 ohm impedance give out even volumes near 10 mV.
I have tried this kind of combination and found out that 
SB16 microphone input is practically useless with all 600 ohms
microphones I have tried!

In normal microphone operation with typical soundcard configuaration
nothign in the system is 600 ohms, so in my point of view it is
very msleading to even write 6000 ohms impedance to the soundcard technical
specs on the microphone input because it is not 600 ohms in impedance
and does not even work well with 600 ohms microphones. But that's
typical marketing where technical facts do not need to be correct
to sell lots of cards.

The input impedance of SB16 microphone input itself is few kilo-ohms
(I don't have the exact figure in my mind). The combination of typical
$2 multimedia microphone connected to soundcard input has around
2 kohms impedance. The fact is that in normal use you see 600 ohms nowhere
else than in misleading technical specs supplied with the soundcard !

-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/